Today, many home and business owners require a security system for protection of valuable assets. Such systems can be complex and difficult to set up and are often inflexible because necessary modifications are difficult to implement. In addition, systems that have central control points can be compromised if the central control point is destroyed or otherwise disabled. Existing systems are also not conductive to integration with multiple security technologies, such as those incorporated with garage door openers, video surveillance equipment, and so on.
Recently, home and business security systems have started to evolve from proprietary, wired approaches toward open standards and wireless systems. Ideally, a system would employ devices such as, but not limited to, controllers, monitors, alarms, communication mechanisms, etc., integrated using a secure communication protocol. There are several secure communication protocols on the market today.
In the early 1970's, a private key encryption system called Data Encryption Standard algorithm (DES) was introduced, which uses a fifty-six (56) bit key to encrypt and decrypt information and communication. DES splits a message into blocks and then encodes each block. DES is no longer considered adequately secure because a 56 bit key can be broken in a relative short time by trying every possible key. DES has since been superseded by the Advanced Encryption Standard (AES), using what is known as the Rijudael algorithm. AES operates with 128, 192 or 256 bit keys. These keys are considered long enough to be safe for the foreseeable future as they would take millions of millions of years for the fastest currently available computers to break.
A second current method for protecting data and communication, is public key encryption, which has been around for approximately twenty-five (25) years. Public key encryption involves the use of two keys: a public key, known to everyone, and a private key, known only to the recipient of a message. Although public key encryption is very effective, there are several drawbacks when it is applied in the realm of digital communication and content storage. First, public key encryption is computationally expensive, i.e. public key systems require such significant computational capacity they are normally only used to implement a key exchange process within a private key encryption system, not to encrypt the body of a message. This process requires a two-way communication, which is not necessarily available in devices incorporated into a security system. Secondly, once the private key of a public key system has been compromised, the system becomes a shared key system. Thirdly, once a public key system has been compromised, there is no practical method for “revoking” the compromised private key.
A recent development in the field of encryption of digital data and communication is broadcast encryption. Broadcast encryption is based upon a key management block (KMB), which is a block of data sent at the beginning of a broadcast or is prerecorded on blank media during the manufacturing process. One of the largest advantages to broadcast encryption is that two devices, which might be previously unknown to each other, can agree upon a key over a one-way communication path. This advantage makes broadcast encryption ideal for the communication between two security system components.
The International Business Machines Corporation (IBM) of Armonk, N.Y., a leader in broadcast encryption, has developed a data encryption system referred to as eXtensible Content Protection (xCP) designed for networks and media distribution. This technology is based on broadcast encryption and supports the notion of a trusted domain that groups together compliant devices. Content can freely move among devices within the trusted domain but is useless to devices that are outside of the domain. xCP provides a cryptographically strong yet extremely flexible model for access to copy-protected content within a network of devices such as a home or business security system.
Based on IBM's experience with broadcast encryption, xCP was designed to meet the following requirements:
1. Cryptographically strong;
2. Easy to use, if not transparent, to consumers;
3. Low compute requirements;
4. Exclusion/renewal in the case of a breach:
5. Compatible with rights management and other copy protection systems; and
6. Encourages the implementation of new content owner business models. Extensible content protection (xCP) makes use of the key management scheme described by broadcast encryption and can be thought of as a superset of the successful content protection technology used and licensed today by IBM on DVDs, High Definition DVDs (HDVDs) and Compact Disks (CDs) called Content Protection for Recordable Media (CPRM).
Public-key based systems, which require devices to have a two-way conversation to establish a key, are almost impossible to completely divorce from an underlying transmission protocol. The IBM xCP Cluster Protocol may be the first system directed to peer devices based upon broadcast encryption as the underlying cryptographic technology. Devices that implement the xCP Cluster Protocol and its broadcast encryption mechanisms are said to “bind” the content they protect to a particular entity (e.g. a home network or cluster) by encrypting the content with a different key, called the binding key (Kb), than the one produced by processing a KMB, as explained below. All current approaches to binding a piece of content to a particular entity, regardless of whether it is a piece of media, a device, or a user, is through one level of indirection in the calculation of the encryption keys. In these cases, the procedure to encrypt a piece of content is roughly the following:                1. Extract a Management Key (Km) by processing the KMB.        2. Perform a one-way function to a piece of data that uniquely identities the entity this content is being bound to (or the “IDb”), using Km and resulting in a binding key (i.e. Kb=G(Km, IDb)).        3. Choose a random title key (Kt) for this piece of content and encrypt it using Kb, resulting in an encrypted title key (EKt) (i.e. EKt=E(Kb, Kt)).        4. The content is encrypted with the Kt and then the encrypted content is stored in conjunction with the EKt.Once the procedure has been implemented, any compliant device that has access to the same KMB, IDb and EKt can decrypt a communication or content by reproducing the same Kb and decrypting Kt.        
In various binding scenarios there is more than one piece of content that is bound to the same entity and, at the same time, either the KMB or IDb can change. The result of this is that the value of Kb changes and thus all the existing title keys need to be re-encrypted with the new value of Kb—otherwise, no device would be able to open the content again. It should be noted that encrypted content of this nature is routinely exchanged and/or copied between entities which participate in the described binding scheme.
What is needed is a home security system implemented according to a broadcast encryption scheme. In this manner, devices can be added and removed from the system and there is no requirement that any particular device remain in communication with the system.